1. Field of the Invention
The present invention relates to a redundancy circuit for series-connected diodes, which can be functionally substituted for a broken diode in a circuit composed of a plurality of diodes connected in series.
2. Description of the Related Art
A number of diodes, such as light emitting diode, are arranged in array for usage of a display. There is a possibility that part of these diodes are broken during use. A conventional art for coping with breakage of a diode, e.g., Japanese Patent Unexamined Publication (kokai) JP-A-2-244685 (1990), discloses a protection circuit for a laser diode, which is designed to detect the temperature of the laser diode. When the detected temperature is in a given range of temperature, the laser diode is supplied with a current based on a diode driving signal. If the detected temperature exceeds a maximum temperature, the current is shut down by the driving signal.
The protection circuit described above is a circuit for preventing a diode from breaking due to rise of temperature. Several other protection circuits for protecting a diode from a surge, over current or abnormal temperature are proposed. Since these circuits aim at preventing failure, once a diode is broken, an interlocking circuit will halt the whole apparatus.
An apparatus, which is configured of a number of diodes connected in series, has an advantage of easy wiring of the diodes. However, if one or more diodes among them are broken down without any conduction so as to open the circuit, no current can pass through the whole series-connected diodes, resulting in malfunction of the apparatus. Meanwhile, even under a condition of partial damage of the diodes, there are needs for continuous operation of the apparatus using the remaining diodes. In particular, a light-emitting panel or a display panel, in which a number of light emitting diodes are connected in series and arranged in array, could not lose the function even though a few diodes are broken down.
In another case one or more diodes among the array of diodes are broken down into an internal short-circuit, reduction of resistance may cause the broken diode to heat up, thereby causing damage to the neighboring diodes. In this case there are also needs for continuous operation of the whole apparatus by shutting off the diode being short-circuited.